// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build !unix

package bio

func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
	return nil, false

// backing memory is read-only.
func (r *Reader) Slice(length uint64) ([]byte, bool, error) {
	if length == 0 {
		return []byte{}, false, nil
	}

	data, ok := r.sliceOS(length)
	if ok {
		return data, true, nil
	}

	data = make([]byte, length)
	_, err := io.ReadFull(r, data)
	if err != nil {
		return nil, false, err
	}
	return data, false, nil
}

)

// This file contains the helper "MReader", a wrapper around bio plus
// an "mmap'd read-only" view of the file obtained from bio.SliceRO().
// MReader is designed to implement the io.ReaderSeeker interface.
// Since bio.SliceOS() is not guaranteed to succeed, MReader falls back
// on explicit reads + seeks provided by bio.Reader if needed.

type MReader struct {
	f        *os.File
	rdr      *bio.Reader
	fileView []byte
	off      int64
}

//	OpenBSD   unlimited
var mmapLimit int32 = 1<<31 - 1

func init() {
	// Linux is the only practically concerning OS.
	if runtime.GOOS == "linux" {
		mmapLimit = 30000
	}
}

func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
	// For small slices, don't bother with the overhead of a
	// mapping, especially since we have no way to unmap it.
	const threshold = 16 << 10
	if length < threshold {
		return nil, false